1. Field of the Invention
The present invention generally relates to an antenna device, and especially relates to an antenna device that includes a ground plate that is shaped like a plate, and a feeding unit that extends at a predetermined angle from the ground plate for a predetermined length, the feeding unit being prepared perpendicular to the ground plate.
2. Description of the Related Art
[Background of the Invention]
In recent years and continuing, radio communications technology using UWB (ultra-wide band) attracts attention since radar positioning and communications with a large transmission capacity are possible. As for UWB, the U.S. FCC (Federal Communications Commission) allowed use of a 3.1–10.6 GHz band in 2002.
Communications at UWB are performed by sending a pulse signal using a wide frequency band. Accordingly, an antenna device used for UWB has to be capable of receiving a wide band signal.
For UWB communications, at least in the 3.1–10.6 GHz frequency band approved by the FCC, an antenna device consisting of a ground plate and a feeder is proposed (Non-patent Reference 1).
FIGS. 1A and 1B show structures of conventional antenna devices.
An antenna device 10 shown in FIG. 1A is constituted by a feeding unit 12 in the shape of a circular cone arranged on a ground plate 11 with the top (apex) of the circular cone facing the ground plate 11.
Here, the circular cone is set up such that the side of the circular cone and an axis 13 that is perpendicular to the ground plate 11 make an angle θ. A desired antenna device property is obtained by setting the angle θ.
An antenna device 20 shown in FIG. 1B is constituted by a feeding unit 22 in the shape of a teardrop that consists of a circular cone 22a, and a sphere 22b inscribed in the circular cone 22a. Here, the feeding unit 22 is arranged on the ground plate 11 with the top of the circular cone 22a facing the ground plate 11.
[Non-patenting Reference 1]
“An Omnidirectional and Low-VSWR Antenna for the FCC-Approved UWB Frequency Band”, published by The Institute of Electronics, Information and Communication Engineers, B-1–133, page 133, Takuya Taniguchi and Takehiko Kobayashi (The Tokyo Electric. University) (Presented on Mar. 22, 2003 at classroom B201).
[Description of the Invention]
[Problem(s) to be Solved by the Invention]
Nevertheless, the conventional wideband antenna devices structured by feeding units that are in the shape of a circular cone and teardrop formed on the plate-like ground plate tend to be large in size. Accordingly, an antenna device having smaller dimensions is desired.